Actuator mechanisms such as shown in U.S. Pat. No. 2,858,097 are known and have been sold commercially by the assignee of that patent for many years and have represented a commercially viable product. However in the years since that valve actuation mechanism was introduced increasing demands on the capabilities of the valve and the actuator have been experienced. Accordingly, there exists a need for a valve which has improved operational characteristics relative to the older valves such that tighter seals can be made and for a valve which has actuator mechanisms which are more maintenance free and less susceptible to environmental contamination.